Contactless IC (integrated circuit) devices, also known as chip cards or smart cards, operate on the basis of communication by an electromagnetic field with a read and/or write interrogating device, generically referred to as a reader.
In contactless IC device applications, the reader typically transmits an electromagnetic carrier wave having a carrier frequency of 13.56 MHz. This transmitted carrier wave serves on the one hand to power the contactless device, which thus derives by induction the energy required for its operation, and on the other hand to set up a communication between the device and the reader according to an established communication protocol. Thus, when the contactless device penetrates into the transmission field of the reader, it communicates with the latter by a modulation operation which consists of modifying at least one parameter of the carrier. The modulation index for ASK modulation carrier waves typically ranges anywhere from between 7-30%. The wide range of acceptable modulation indices has caused compatibility issues with conventional demodulator circuits and thereby increased demodulator requirements resulting in increasingly complex demodulators.